Allograft dysfunction is caused by both alloantigen-dependent and alloantigen-independent factors. Ischemia/reperfusion (I/R) injury is perhaps the most important alloantigen-independent factor contributing to early acute as well as chronic organ graft dysfunction. A major advance would be to identify novel strategies to prevent the early and late sequelae of this injury on cadaver transplants. This is the long-term goal of the research proposal. The exact mechanisms of how I/R injury contributes to graft dysfunction remain unclear. Recent experimental data suggest that CD4+ T lymphocytes may play an important role in this injury even in the absence of alloantigen. In that regard, our laboratory, in collaboration with the Surgical Research Laboratory (Dr. N. L. Tilney), recently showed that the CD28-B7 T cell costimulatory pathway may play an important role in I/R injury. At present, the role of the CD40L- CD40 pathway in cold I/R injury in unknown. The main purpose of this proposal is to study the role and mechanisms of this pathway in I/R injury, at a cellular, molecular and whole animal level using a model of renal cold I/R injury. Moreover, we plan to determine if there is synergy between CD40L-CD40 and CD28-B7- 1/B7-2 in I/R injury. Finally, our studies will help further define the role and mechanisms of T cell activation in I/R injury.